Online

Cullen, Erin R.

Neuroscience Graduate Program

2023

Ph. D.

Gene variants that hyperactivate the mTOR signaling pathway are a major cause of treatment-resistant epilepsy. The mTOR pathway influences neuron function through two distinct complexes, mTORC1 and mTORC2. Pten loss of function (LOF) hyperactivates both mTOR complexes, and is thus a useful model for testing the effects of independent mTORC1 or mTORC2 hyperactivity on epilepsy and underlying neuropathology. Here, we evaluated the impact of genetic inactivation of the mTOR complexes in two mouse models of Pten LOF-driven epilepsy. In a germline GFAP-driven Pten LOF model targeting neurons in the dentate gyrus and cerebellum, a mild epilepsy phenotype was not rescued by mTORC2 inactivation, and early mortality was exacerbated by mTORC1 inactivation. mTORC2 inactivation attenuated morphological and electrophysiological consequences of Pten LOF in dentate gyrus granule neurons, but did not rescue ectopic synaptic connections in the dentate granule cell layer. In a synapsin-driven focal cortical Pten LOF model, genetic inactivation of neither mTORC1 nor mTORC2 fully rescued spontaneous seizures or interictal epileptiform activity, although simultaneous inactivation of mTORC1 and mTORC2 fully did rescue these phenotypes. Further experiments showed that while either mTORC1 or mTORC2 inactivation attenuated the impact of Pten LOF on neuron size and membrane excitability, mTORC1 inactivation did not normalize cortical interneuron loss or increased excitatory synaptic activity, and mTORC2 inactivation may increase excitatory synaptic strength. Overall, these results indicate that normalization of neuron size and membrane excitability does not substantially impact epilepsy development in Pten LOF, and that mechanisms downstream of either mTORC1 or mTORC2 can cause epilepsy. Thus, the potential roles of both mTORC1 and mTORC2 should be considered when modeling and treating mTOR-associated epilepsy.